Use Of Surface-Enhanced Raman Scattering In The Investigation Of The Adsorption Features Of Several Kinds Of Azobenzene Dye Molecules

The structure of azo dyes has attracted considerable attention in recent times, since they represent the largest class of dyes used in industry, and also has extensive applicability in analytical chemistry as acid-base, redox and metallochromic indictors. Moreover, azo dyes find wide applicability in reversible optical data storage. The storage process utilizes the light induced trans-cis-trans isomerization of the azo dye, thereby utilizing the local variation of the refractive index of the medium. The photoinduced changes in polarity and molecular structure have led to widespread application of azobenzene derivatives as reversible molecular switch devices. There were many literature on the studies of the structure of Azo dyes by means of various spectroscopic and photochemical methods including UV-vis absorption, infrared(IR),Raman spectroscopy and photochemical. However, there is no report about the adsorption character of azo dyes. Surface-enhanced Raman Scattering(SERS) is widely used as a highly powerful analytical tools to investigate molecular structure and interaction between molecules and metal surface resulting in strongly increased Raman signals from molecule which have been attached to nanometer sized metallic structures. The SERS spectra of azobenzene, methyl red and methyl red salt adsorbed on the different substrate. The objective of this work was to obtain information about spectral properties of the three kind of azo dyes and use these information to gain an overall picture of the nature of the adsorption sites on these metal surfaces. This paper includes three sections as following: In the first section, the discovery, characteristics, mechanisms, and use of SERS are simply summarized. In the second section, the SERS spectra of azobenzene molecules adsorbed on silver sol and silver mirror were investigated. The analysis of spectra shows that azobenzene molecules adsorbed on the metal surfaces through the phenyl, but the adsorption of azobenzene molecules were different. Azobenzene molecules stand on the surface of silver sol, compared with lie on the surface of silver mirror, which could be due to the difference of interaction between the solvent molecules and azobenzene molecules. In the third section, the SERS spectra of methyl red salt and methyl red molecules in silver sol, methyl red on silver mirror and copper were obtained. The analysis of spectra shows that all of these molecules adsorbed on the metal surfaces through the phenyl, and the Dimethylamino group of these molecules are far from metal surfaces. Methyl red molecules had the largest intensity in silver sol.